ACTION OF REAGENTS. 137 



6. Prove the fermentative nature of curdling by mixing the 



rennet with a little water and boiling it before adding 

 it to the milk. The milk will not curdle because the 

 ferment has been destroyed. 



7. Proteids. Strained whey is provided for you. Acidulate 



some with acetic acid no caseinogen boil thoroughly 

 there will be very little coagulum lactalbumin filter 

 and test the filtrate for 



8. Sugar in whey by means of Fehling solution. 



9. Add ammonium oxalate solution to some whey, a light pp 



indicates calcium salts. The chief salts. Test also for P 2 O5. 

 pg. 160. 



10. Guaiacum test. To some fresh milk add a few drops of 



fresh tincture of guaiacum, agitate, add half a volume of 

 peroxide of hydrogen, a blue colour due to oxygen 

 liberated by proteids turning the resin blue. 



11. Repeat 10 with boiled milk the blue colour is not given 



due to changes in the proteid. 



12. Fat in milk. The milk globules have already been examined 



(Histology). To 2 cm milk add 2 or 3 vols. of ether, cork 

 the tube, wrap it in a damp cloth or folds of blotting- 

 paper to prevent heating by the hand, and shake thoroughly 

 for 30 seconds there will be no change. Add 1 or 2 

 drops of NaOH sol., shake again ; the ether will now 

 dissolve the fat and the milk will lose its opacity. Hand 

 the tube to the laboratory attendant. 



Estimation of cream. Whole milk is centrifuged for 

 5 minutes in a Watson-Laidlaw cream tester. The per- 

 centage is read off directly as solid cream in the graduated 

 tubes of the instrument. There should be about 12 per 

 cent, present. 



